Preparation method of thermal shock resistant magnesium aluminate spinel transparent ceramic

Abstract

The invention discloses a preparation method of thermal shock resistant magnesium aluminate spinel transparent ceramic, and belongs to the technical field of ceramic materials. The preparation method comprises the following steps: (1) synthesizing crystalline MgAl2O4 nano powder by adopting an additive-free hydrothermal method; (2) depolymerizing the powder, performing water-based gel casting to prepare a green body, and performing staged debonding treatment on the green body; (3) carrying out two-step vacuum presintering on the green body; (4) carrying out hot isostatic pressing densification treatment in a subgrain growth temperature region of 1380-1420 DEG C; and (5) carrying out annealing treatment on the densified ceramic. High-purity crystalline powder is synthesized through an additive-free hydrothermal method, grain boundary impurities are eliminated, and the intermediate infrared transmittance is remarkably improved; by combining the synergistic effect of optimized two-step pre-sintering and hot isostatic pressing in a sub-grain region, precise refinement of the grain size is realized; and finally, the bending strength, the fracture toughness and the critical thermal shock temperature difference of the material are greatly improved under the strengthening mechanism of ultrafine grains and defect-free grain boundaries.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a heat shock resistant magnesium aluminate spinel transparent ceramic and belongs to the technical field of ceramic materials. BACKGROUND

[0002] Magnesium aluminate spinel (MgAl2O4) transparent ceramics have become the core optical materials for extreme environments such as the fairing of hypersonic aircraft and high-energy laser windows due to their excellent optical transmittance, high hardness and good thermal mechanical properties. The heat shock resistance of the magnesium aluminate spinel transparent ceramics directly determines the service reliability of the devices under severe temperature changes. Currently, the industry mainly adopts the coprecipitation method or the solid phase reaction method to prepare the powder, and combines the hot-pressing sintering or vacuum sintering with the hot isostatic pressing (HIP) process to realize densification. However, the precipitants (such as NH4HCO3) and dispersants (such as PEG) necessary for the coprecipitation method can introduce alkali metal ions and organic residues, form a grain boundary glass phase at high temperatures, cause light scattering and mechanical property degradation, and the solid phase method introduces Fe / Zr and other abrasion impurities due to multiple ball milling, greatly reduces the optical uniformity of the material, and seriously restricts high-end applications.

[0003] In the patent CN115466103B, a magnesium aluminate spinel heat storage ceramic and a preparation method thereof are disclosed. The magnesium aluminate spinel heat storage ceramic is obtained by using fused magnesia, alpha-Al2O3 and the like as raw materials, and adding CaF2 and TiO2 as sintering aids. Although the technical scheme realizes a high working temperature (>1000 DEG C) and good heat shock resistance, the introduction of the sintering aids inevitably leads to the formation of a grain boundary glass phase, thereby increasing the light scattering effect and reducing the transmittance in the mid-infrared band. In addition, the grain size is difficult to accurately control in the sintering process, which limits the application of the magnesium aluminate spinel transparent ceramic in the high-end optical field.

[0004] The patent CN102863247B discloses a preparation method of a dense magnesium aluminate spinel refractory aggregate. Light-burned magnesite powder and alumina powder are used as raw materials, the pre-sintered and crushed materials are immersed in saturated lime water or calcium acetate solution, and then the dense magnesium aluminate spinel aggregate is obtained through high-temperature sintering. Although the method improves the density and heat shock resistance of the material, Fe / Zr and other impurities are introduced due to multiple ball milling and pre-sintering processes, which greatly reduces the optical uniformity of the material. At the same time, the preparation process is complex and the energy consumption is high, which is difficult to meet the requirements of high purity and low cost of high-end transparent ceramics.

[0005] In summary, the existing process has a fundamental contradiction among powder purity-grain size-densification: high-purity powder leads to grain coarsening due to insufficient sintering activity or high preparation cost; grain refinement requires sacrificing densification or introducing optical harmful additives; hot isostatic pressing post-processing can improve densification, but high-temperature working conditions exacerbate grain growth. How to simultaneously achieve "no impurity pollution" (metal impurities < 50 ppm), "submicron grain precision control" (< 500 nm), and "theoretical limit density" (> 99.99% TD) has become the core technical bottleneck to break through the thermal shock resistance ceiling of magnesium aluminate spinel transparent ceramics, and is also an industrialization problem to be solved by the present application. SUMMARY

[0006] The technical problem solved by the present application is to overcome the shortcomings of the prior art and provide a preparation method of a thermal shock resistant magnesium aluminate spinel transparent ceramic with extremely low impurity pollution and densification.

[0007] The technical solution adopted by the present application to solve the technical problem is: a preparation method of a thermal shock resistant magnesium aluminate spinel transparent ceramic, characterized by the following preparation steps:

[0008] (1) synthesizing crystalline MgAl2O4 nano-powder by an additive-free hydrothermal method;

[0009] (2) preparing a green body by water-based injection molding after depolymerization of the powder, and performing stage-by-stage debinding treatment on the green body;

[0010] (3) performing two-step vacuum pre-sintering on the green body;

[0011] (4) performing hot isostatic pressing densification treatment at a sub-grain growth temperature of 1380-1420℃;

[0012] (5) performing annealing treatment on the densified ceramic.

[0013] The present application eliminates grain boundary impurities by synthesizing high-purity crystalline powder by an additive-free hydrothermal method, significantly improves the mid-infrared transmittance; combines optimized two-step pre-sintering and sub-grain zone hot isostatic pressing synergy to achieve precise refinement of grain size; finally, under the strengthening mechanism of ultra-fine grain and defect-free grain boundary, the bending strength, fracture toughness and critical thermal shock temperature difference of the material are greatly improved, the technical bottleneck of high-purity, submicron grain and theoretical density is overcome, and the severe demand for material thermal shock resistance under extreme working conditions is met.

[0014] Preferably, the particle size of the crystalline MgAl2O4 nano-powder in step (1) is 20-50 nm, and the specific surface area is 80-120 m 2 / g. 2This particle size and high specific surface area can significantly enhance the sintering activity of the powder, thereby reducing the second-step pre-sintering temperature and shortening the densification time.

[0015] Specifically, the specific preparation process of the additive-free hydrothermal method in step (1) includes:

[0016] (a) using aluminum isopropoxide (99.995% purity or greater) and magnesium acetate (99.99% purity or greater) as precursors to form a sol in ultrapure water (18.2 MΩ·cm resistivity or greater), and adjusting the pH to 9-10 with aqueous ammonia;

[0017] (b) reacting in a polytetrafluoroethylene-lined reactor at 240° C. to 260° C. for 12 to 24 hours;

[0018] (c) The product was centrifugally washed until the filtrate conductivity was <5 μS / cm, and then dried by supercritical CO2 at 40°C and 10 MPa to obtain crystalline MgAl2O4 nanopowder.

[0019] High-purity precursors and ultrapure water are used to eliminate metal impurities at the source; a crystalline spinel phase is directly generated through a hydrothermal reaction to avoid abnormal grain growth caused by amorphous phase transformation; organic residues are removed through washing; and supercritical CO2 drying eliminates hydroxyl group agglomeration while maintaining nano-scale dispersion, providing a highly active powder foundation for subsequent dispersant-free molding.

[0020] Specifically, the specific process of water-based gelcasting described in step (2) is as follows: dispersing the depolymerized crystalline MgAl2O4 nanopowder in ultrapure water to form a slurry with a solid content of 45 vol% to 50 vol%, adding the gel system, ultrasonically dispersing at 350W to 450W and vacuum degassing, and then curing at 62°C to 67°C to form the green body; the green body is subjected to cold isostatic pressing at 200MPa to 250MPa and 25°C to 35°C until the density reaches 2.15g / cm 3 .

[0021] This molding process achieves uniform distribution of powder without hard agglomeration through the synergistic effect of high solid content slurry and ultrasonic dispersion; the curing molding temperature is precisely controlled to form a three-dimensional network skeleton, and combined with cold isostatic pressing pressure, the green density reaches 2.15g / cm 3 (60% TD), eliminating the internal density gradient, providing a green billet foundation with low shrinkage stress for the two-step sintering, and avoiding cracking and deformation during high-temperature densification.

[0022] Specifically, the gel system is a composite gel system of acrylamide and N,N'-methylenebisacrylamide, with the acrylamide content ranging from 5wt% to 7wt% of the slurry, and the N,N'-methylenebisacrylamide content ranging from 0.5wt% to 0.7wt% of the slurry. This precise ratio of acrylamide to N,N'-methylenebisacrylamide enhances the strength of the three-dimensional network formed during curing and molding, resulting in higher compressive strength for the green body. Furthermore, the low addition amount reduces organic residues, resulting in a carbon residue of less than 15ppm after pre-sintering, eliminating grain boundary carbon contamination.

[0023] Preferably, the crystalline MgAl2O4 nanopowder is subjected to surface protonation treatment with 0.0008 mol / L to 0.0012 mol / L HNO3 solution before water-based gelcasting to enhance dispersibility.

[0024] Specifically, the specific process of the surface protonation treatment is: dispersing the depolymerized crystalline MgAl2O4 nanopowder in a 0.0008mol / L to 0.0012mol / L nitric acid solution at a solid-liquid ratio of 1:9 to 12; stirring at room temperature until the conductivity stabilizes at 15±2μS / cm, and then terminating the treatment; washing the precipitate obtained by solid-liquid separation and vacuum drying it at 35°C to 45°C to complete the treatment.

[0025] This process uses precise protonation with a specific concentration of nitric acid to shift the powder's zeta potential from -15mV to +35mV, creating strong electrostatic repulsion in the absence of a dispersant. Low-temperature vacuum drying preserves surface active groups and reduces slurry viscosity. The resulting green compact is more uniform, ensuring no impurity segregation at the grain boundaries of the sintered body. Furthermore, the selected endpoint prevents aluminum dissolution caused by excessive acid etching.

[0026] Specifically, the staged debonding treatment in step (2) is as follows: heating to 400-450°C at 0.5-1°C / min in an air atmosphere, holding for 90-120 minutes; then heating to 600-650°C at 1-2°C / min, holding for 60-90 minutes, with an air flow rate of ≥100 mL / min·g. The green body is placed in an air atmosphere tubular furnace, where acrylamide monomer is eliminated by low-temperature oxidation at 400-450°C, followed by a medium-temperature carbon removal at 600-650°C to completely crack the MBAM cross-linked network. After this treatment, the organic residue content of the green body is reduced from 7.7 wt% to <0.01 wt%, and the carbon residue after pre-sintering is <15 ppm, eliminating closed pores and light scattering defects caused by grain boundary carbon contamination.

[0027] Specifically, the two-step vacuum pre-sintering in step (3) includes:

[0028] Raise the temperature to 1500-1550°C at a rate of 8-12°C / min and keep the temperature under a vacuum of ≤0.001 Pa for 25-35 minutes;

[0029] The temperature is then immediately lowered to 1300° C. to 1350° C. and maintained for 15 to 25 hours to obtain a semi-dense ceramic with a density greater than 99.3% TD and a grain size less than 300 nm.

[0030] This two-step vacuum pre-sintering process quickly eliminates open pores through high-temperature short-time insulation, combined with ultra-low-temperature long-time insulation to inhibit grain boundary migration, to obtain semi-dense ceramics with a density >99.3% TD and a grain size <300nm, reserving structural space for subsequent sub-grain area HIP to achieve ultimate densification.

[0031] Preferably, the hot isostatic pressing pressure in step (4) is 180 MPa to 200 MPa, and the holding time is 55 min to 65 min.

[0032] This hot isostatic pressing process applies a high pressure of 180MPa to 200MPa for 55min to 65min in the sub-grain growth temperature zone (1380℃ to 1420℃), using isostatic pressure rather than high-temperature thermal energy to drive material flow, eliminating the ultimate closed pores with a size of <10nm, and increasing the ceramic density to ≥99.997%TD. At the same time, the grain size is controlled at 300nm to 350nm, achieving "zero grain length and high densification", providing dual guarantees of defect-free grain boundaries and ultrafine grains for high thermal shock resistance.

[0033] Preferably, the annealing in step (5) is carried out in an air atmosphere at a temperature of 1100° C. to 1200° C. for a holding time of 100 min to 150 min. This annealing process can release lattice residual stress, while promoting the ordering of trace oxygen vacancies at the grain boundaries, thereby improving the optimized grain boundary bonding strength and fracture toughness.

[0034] The magnesium-aluminum spinel transparent ceramic prepared by the present invention has a grain size of 300nm to 350nm, a linear transmittance of ≥86.7% at a wavelength of 4μm (thickness of 3mm), a three-point bending strength of ≥400MPa, and a critical thermal shock temperature difference ΔTc of water quenching of ≥500℃. The fracture toughness is ≥2.8MPa·m 1 / 2 .

[0035] Compared with the existing technology, the beneficial effects of the preparation method of thermal shock resistant magnesium aluminum spinel transparent ceramics of the present invention are as follows: the present invention synthesizes high-purity crystalline powder through an additive-free hydrothermal method, eliminates grain boundary impurities from the source, and significantly improves optical transmittance; innovatively adopts a two-step pre-sintering and sub-grain zone hot isostatic pressing collaborative process to precisely control grain ultrafineness while achieving theoretical limit densification, and completely solves the technical contradiction between high purity, ultrafine grains and full density; ultimately, excellent mechanical properties and thermal shock resistance are obtained, the three-point bending strength and fracture toughness are greatly improved, and the critical thermal shock temperature difference of water quenching breaks through the industry bottleneck, providing the first ceramic material with both high light transmittance and thermal shock resistance for extreme working conditions, filling the international technological gap. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to specific embodiments, wherein embodiment 1 is the best embodiment.

[0037] Example 1

[0038] 1) A crystalline nanopowder was synthesized directly using an additive-free hydrothermal method. Recrystallized aluminum isopropoxide (99.996%) and magnesium acetate (99.994%) were used as precursors. A homogeneous sol was formed by magnetic stirring in ultrapure deionized water with a resistivity of 18.25 MΩ·cm. The pH was then adjusted to 9 with ammonia to initiate the reaction. The sol was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and reacted at 250°C and pressure for 18 hours, generating a spinel phase through a dissolution-recrystallization mechanism. The resulting product was centrifuged and repeatedly washed with ultrapure water for more than 10 times until the filtrate conductivity was below 5 μS / cm, completely removing residual ions such as acetate. Finally, supercritical CO₂ drying at 40°C and 10 MPa yielded fluffy, agglomerated crystalline MgAl₂O₄ nanopowder with an average particle size of 37 nm and an average surface area of ​​10⁻³ m⁻¹. 2 / g, the powder was deagglomerated by low-energy air flow milling under argon protection and dispersed in a 0.001 mol / L HNO3 solution at a mass solid-to-liquid ratio of 1:10; the treatment was terminated when the conductivity stabilized at 15±2μS / cm at room temperature; the precipitate obtained by solid-liquid separation was washed and vacuum-dried at 40°C to complete surface protonation treatment, thereby enhancing its electrostatic dispersion stability in water.

[0039] 2) In the shaping stage, a water-based injection molding process without dispersant was used to take advantage of the high surface charge characteristics of the powder itself: the depolymerized powder was added to ultrapure water in several portions, and after being dispersed by a 400W ultrasonic probe, a slurry with a solid content of 47vol% was formed. 6wt% of acrylamide and 0.6wt% of crosslinking agent MBAM were added as the gel system. The slurry was injected into the mold after vacuum degassing and cured at 65℃ to form a gel blank. The obtained gel blank was treated by cold isostatic pressing at 230MPa and 30℃ until the density reached 2.15g / cm 3 The green body was placed in an alumina crucible and heated to 450℃ at a rate of 0.8℃ / min and held for 120min, then heated to 650℃ at a rate of 1.5℃ / min and held for 90min, with a flow of 150mL / min·g of dry air throughout the process.

[0040] 3) In the pre-sintering stage, a two-step vacuum sintering process was used: the first step was to rapidly heat to 1520℃ at a rate of 10℃ / min and hold for 30min under a vacuum of ≤0.001Pa; the second step was to immediately cool to 1320℃ and hold for 20h.

[0041] 4) A high-pressure argon gas of 190MPa was applied at a low temperature window of 1400℃ and held for 60min, and then the ceramic was annealed in air at 1150℃ for 60min to complete the preparation.

[0042] Example 2

[0043] The basic process was the same as in Example 1, except that in step 2) the gel system was only added with 6wt% of acrylamide.

[0044] Example 3

[0045] The basic process was the same as in Example 1, except that in step 1) the obtained crystalline MgAl2O4 nano-powder was not treated by surface protonation in HNO3 solution.

[0046] Example 4

[0047] 1) Direct synthesis of crystalline nanopowder by hydrothermal method without additive: 99.996% purity isopropyl aluminum and 99.994% purity magnesium acetate were used as precursors. The sol was formed by magnetic stirring in 18.25 MΩ·cm ultrapure deionized water, and the pH was adjusted to 9 with ammonia water to initiate the reaction. The sol was transferred to a polytetrafluoroethylene-lined hydrothermal reactor, and the reaction was carried out at 240°C for 24 hours under high temperature and pressure. The spinel phase was directly generated by the dissolution-recrystallization mechanism. The product was separated by centrifugation and washed repeatedly with ultrapure water for more than 10 times until the conductivity of the filtrate was less than 5 μS / cm, and the residual ions such as acetate were completely removed. Finally, the fluffy and non-hard agglomerated crystalline MgAl2O4 nanopowder was obtained by supercritical CO2 drying technology at 40°C and 10 MPa, with an average particle size of 20 nm and an average specific surface area of 120 m 2 / g. The powder was dispersed in 0.0008 mol / L HNO3 solution at a mass ratio of 1:9 under argon protection, and the conductivity was stabilized at 15±2 μS / cm after stirring at room temperature. The precipitate obtained by solid-liquid separation was washed and dried in vacuum at 35°C to complete the surface protonation treatment, which enhanced the electrostatic dispersion stability in water.

[0048] 2) In the forming stage, the high surface charge characteristics of the powder were utilized to adopt a water-based injection molding process without dispersant: the depolymerized powder was added to ultrapure water in several portions, and a slurry with a solid content of 45 vol% was formed after strong dispersion by a 350W ultrasonic probe. Acrylamide and 0.5wt% crosslinking agent MBAM were added as the gel system, with a content of 5wt% and 0.5wt% respectively. The vacuum degassed slurry was injected into the mold and cured at 62°C to form a gel body, which was then cold isostatic pressed at 200MPa and 25°C until the density reached 2.15 g / cm 3 to obtain a green body. The green body was placed in an alumina crucible and heated to 400°C at a rate of 0.5°C / min and held for 120 min, then heated to 600°C at a rate of 1°C / min and held for 90 min, with a flow rate of 120 mL / min·g dry air throughout the process.

[0049] 3) The pre-sintering stage adopts a two-step vacuum sintering process: the first step is to rapidly heat to 1500°C at a rate of 8°C / min and hold for 35 min under a vacuum of ≤0.001 Pa; the second step is to immediately reduce the temperature to 1300°C and hold for 25 h.

[0050] 4) Apply 180MPa high pressure argon at a low temperature window of 1380°C and hold for 65 min, and perform 1100°C air atmosphere annealing for 65 min.

[0051] Example 5

[0052] 1) Direct synthesis of crystalline nanopowder by hydrothermal method without additive, the process selects recrystallized isopropyl alcohol aluminum with purity of 99.996% and pure magnesium acetate with purity of 99.994% as precursor, after forming uniform sol by magnetic stirring in ultra-pure deionized water with resistivity of 18.25 MΩ·cm, the reaction is initiated by adjusting pH to 10 with ammonia water. The sol is transferred into a polytetrafluoroethylene-lined hydrothermal reactor, and the spinel crystal phase is directly generated by the dissolution-recrystallization mechanism under the condition of high temperature and high pressure at 260℃ for 12h. The obtained product is centrifuged and washed repeatedly with ultra-pure water for more than 10 times until the conductivity of the filtrate is less than 5μS / cm, and the residual ions such as acetate are completely removed. Finally, the fluffy and non-hard agglomerated crystalline MgAl2O4 nanopowder is obtained by supercritical CO2 drying technology at 40℃ and 10MPa, the average particle size is 50nm, the average specific surface area is 80m 2 / g, and the powder is dispersed in 0.0012mol / L HNO3 solution according to the mass solid-liquid ratio of 1:12 under argon protection; stirring at room temperature until the conductivity is stable at 15±2μS / cm; the obtained precipitate is washed and dried in vacuum at 45℃ to complete the surface protonation treatment, which enhances the electrostatic dispersion stability in water.

[0053] 2) In the forming stage, the high surface charge characteristics of the powder itself are utilized, and a water-based injection molding process without dispersant is adopted: the depolymerized powder is added to ultra-pure water in several times, and a slurry with a solid content of 50vol% is formed after strong dispersion by a 450W ultrasonic probe, and 7wt% of acrylamide and 0.7wt% of crosslinking agent MBAM are added as the gel system. The vacuum degassed slurry is injected into the mold and cured at 67℃ water bath to form a gel blank, and the gel blank is treated by 250MPa cold isostatic pressing at 35℃ until the density reaches 2.15g / cm 3 to obtain a green body. The green body is placed in an alumina crucible, heated to 450℃ at a rate of 1℃ / min and kept for 90min, then heated to 650℃ at a rate of 2℃ / min and kept for 60min, and dry air is introduced at a rate of 150mL / min·g throughout the process.

[0054] 3) The pre-sintering stage is aimed at a two-step vacuum sintering process: the first step is to rapidly heat to 1550℃ at a rate of 12℃ / min, and keep for 25min under a vacuum of ≤0.001Pa; the second step is to immediately reduce the temperature to 1350℃ and keep for 15h.

[0055] 4) Apply 200MPa high-pressure argon gas at a low temperature window of 1420℃ and keep for 55min, and perform 1200℃ air atmosphere annealing for 55min.

[0056] The ceramic sheet samples with diameter Φ 30 mm x thickness 3 mm prepared from Examples 1-5 were subjected to performance tests, with the benchmark group being a commercial magnesium aluminate spinel transparent ceramic (trade name SC-1) from Surmet Corporation, USA; the test standard for linear transmittance (denoted as 4 pm transmittance in Tables 1, 2) was ASTM E424-71, the test standard for three-point bending strength (denoted as bending strength in Tables 1, 2) was ISO 14704:2016, the test standard for fracture toughness (K IC ) was JIS R 1607 (SEPB method), the test standard for critical thermal shock temperature difference (denoted as critical ΔT c ) in Tables 1, 2 was ASTM C1525 (water quenching method), the test standard for grain size was ASTM E112-13, and the residual strength retention rate was the strength retention rate after the sample was subjected to 500°C→25°C water quenching for 10 times. The test results are shown in Table 1.

[0057] Table 1. Performance test results

[0058]

[0059] The ceramic of the present application has been significantly improved in terms of 4 pm band transmittance, bending strength, fracture toughness, grain size refinement, etc.

[0060] Comparative Example 1

[0061] The basic process was the same as in Example 1, except that the process of step 1) was modified as follows: aluminum chloride hexahydrate (AlCl3·6H2O, purity 99.9%) and magnesium chloride hexahydrate (MgCl2·6H2O, purity 99.9%) were used as precursors to prepare a 0.5 mol / L mixed metal salt solution, which was continuously stirred in a 40°C constant temperature water bath and 2 mol / L ammonium bicarbonate (NH4HCO3) solution was added dropwise to pH = 9.0, while 1.0 wt% polyethylene glycol (PEG-6000) was added as a dispersant; the precipitate was aged for 12 hours, then washed by centrifugation until the Cl - concentration of the filtrate was <100 ppm, and the precursor powder was dried at 120°C for 24 hours; finally, the MgAl2O4 powder was obtained by calcination at 800°C in air for 2 hours.

[0062] Comparative Example 2

[0063] The basic process was the same as in Example 1, except that the surface protonation treatment was cancelled, the powder was directly used for gelcasting after depolymerization, and was not treated with HNO3 solution; the sintering process was changed, conventional vacuum sintering was used at 1550°C for 3h instead of the two-step pre-sintering in Example 1; and the HIP treatment temperature was increased to 1550°C.

[0064] Comparative Example 3

[0065] The basic process is the same as that of Example 1, except that in step 3) the parameters of two-step pre-sintering are adjusted as follows: the first step is to heat to 1600°C and keep for 10 min; the second step is to keep at 1350°C for 20 h.

[0066] The performance test results of the comparative examples are shown in Table 2.

[0067] Table 2. Performance comparison table of the present application and comparative examples

[0068]

[0069] The above description is only the preferred embodiments of the present application, and is not intended to limit the present application in other forms. Any person skilled in the art can modify or change the above disclosed technical content to equivalent embodiments. However, any simple modification, equivalent change and modification of the above embodiments made according to the technical essence of the present application without departing from the technical solution content of the present application still belongs to the protection scope of the present application technical solution.

Claims

1. A method for preparing thermal shock resistant magnesium aluminum spinel transparent ceramics, characterized in that: The preparation steps include: (1) Synthesis of crystalline MgAl2O4 nanopowders by a hydrothermal method without additives; (2) deagglomerating the powder and then subjecting it to water-based gelcasting to prepare a green body, and performing a debonding treatment on the green body in stages; (3) performing two-step vacuum pre-sintering on the green body; (4) hot isostatic pressing densification treatment in the subgrain growth temperature range of 1380°C to 1420°C; (5) Annealing the densified ceramics.

2. The method for preparing a thermal shock resistant magnesium aluminum spinel transparent ceramic according to claim 1, characterized in that: The particle size of the crystalline MgAl2O4 nanopowder described in step (1) is 20nm to 50nm, and the specific surface area is 80m 2 / g~120m 2 / g.

3. The method for preparing a thermal shock resistant magnesium aluminum spinel transparent ceramic according to claim 1 or 2, characterized in that: The specific preparation process of the additive-free hydrothermal method in step (1) includes: (a) using aluminum isopropoxide (99.995% purity or greater) and magnesium acetate (99.99% purity or greater) as precursors to form a sol in ultrapure water (18.2 MΩ·cm resistivity or greater), and adjusting the pH to 9-10 with aqueous ammonia; (b) reacting in a polytetrafluoroethylene-lined reactor at 240° C. to 260° C. for 12 to 24 hours; (c) The product was centrifugally washed until the filtrate conductivity was <5 μS / cm, and then dried by supercritical CO2 at 40°C and 10 MPa to obtain crystalline MgAl2O4 nanopowder.

4. The method for preparing a thermal shock resistant magnesium aluminum spinel transparent ceramic according to claim 1, characterized in that: The specific process of water-based gelcasting described in step (2) is as follows: dispersing the depolymerized crystalline MgAl2O4 nanopowder in ultrapure water to form a slurry with a solid content of 45 vol% to 50 vol%, adding the gel system, ultrasonically dispersing at 350W to 450W, vacuum degassing, and then curing at 62°C to 67°C. The obtained green body is subjected to cold isostatic pressing at 200MPa to 250MPa and 25°C to 35°C until the density reaches 2.15g / cm 3 .

5. The method for preparing a thermal shock resistant magnesium aluminum spinel transparent ceramic according to claim 4, characterized in that: The gel system is a composite gel system of acrylamide and N,N'-methylenebisacrylamide, wherein the amount of acrylamide is 5wt% to 7wt% of the slurry, and the amount of N,N'-methylenebisacrylamide is 0.5wt% to 0.7wt% of the slurry.

6. The method for preparing a thermal shock resistant magnesium aluminum spinel transparent ceramic according to claim 4, characterized in that: The crystalline MgAl2O4 nanopowder is first subjected to surface protonation treatment before water-based injection molding. The specific process of the surface protonation treatment is: dispersing the depolymerized crystalline MgAl2O4 nanopowder in a 0.0008mol / L to 0.0012mol / L nitric acid solution at a solid-liquid ratio of 1:9 to 12; stirring at room temperature until the conductivity stabilizes at 15±2μS / cm, and then terminating the treatment; washing the precipitate obtained by solid-liquid separation and vacuum drying it at 35°C to 45°C to complete the treatment.

7. The method for preparing a thermal shock resistant magnesium aluminum spinel transparent ceramic according to claim 1, characterized in that: The staged debonding treatment in step (2) is specifically as follows: heating to 400°C to 450°C at 0.5°C / min to 1°C / min in an air atmosphere, and keeping warm for 90min to 120min; continuing to heat to 600°C to 650°C at 1°C / min to 2°C / min, and keeping warm for 60min to 90min, with an air flow rate of ≥100mL / min·g.

8. The method for preparing a thermal shock resistant magnesium aluminum spinel transparent ceramic according to claim 1, characterized in that: The two-step vacuum pre-sintering in step (3) includes: Raise the temperature to 1500°C~1550°C at 8°C / min~12°C / min and keep it at this temperature for 25min~35min under a vacuum of ≤0.001Pa; then immediately lower the temperature to 1300°C~1350°C and keep it at this temperature for 15h~25h.

9. The method for preparing a thermal shock resistant magnesium aluminum spinel transparent ceramic according to claim 1, characterized in that: The hot isostatic pressing pressure in step (4) is 180 MPa to 200 MPa, and the holding time is 55 min to 65 min.

10. The method for preparing a thermal shock resistant magnesium aluminum spinel transparent ceramic according to claim 1, characterized in that: The annealing in step (5) is carried out in an air atmosphere, the annealing temperature is 1100° C. to 1200° C., and the holding time is 100 min to 150 min.

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